So, the final solution is:
1. enable modular support for AGP in kernel (Device drivers --> Character devices --> /dev/agpgart support), do NOT enable intel AGP support (Intel 440LX/BX/GX, I8xx and E7x05 ...)
- or -
make sure you have only agpgart.ko module in /lib/modules/`uname -r`/kernel/drivers/char/agp:

QuadroFX GO1400, PCI-Express (So, no AGP should be envolved)
Still set NvAgp to 0 in XF86Config, just in case.

When suspending to RAM, system fails to resume.
It starts to, printing 'Linu' , 'Back to C'.
The LCD aspect changes (looks like the video driver tries and fails to restore its state)
Then the system hangs.
Amazingly, Fn-F2 which should turn bluetooth on/off still works
(at least, the blue LED toggles), but with a 2 to 3 second delay !
As if the CPU/Bus/something was overloaded to death.

Furthermore :
* agpgart module is not loaded
* things are fine when nvidia module is not loaded.
* Suspend to RAM seems to work with the vesa driver, but I cannot reach the desired resolution (1680x1050)
* Getting rid of modules (tg3, ehci-hcd) sharing the IRQ (11 in my case) does not change anything

Apart from this, everything's fine,
but not being able to suspend a laptop ...

So, the final solution is:
1. enable modular support for AGP in kernel (Device drivers --> Character devices --> /dev/agpgart support), do NOT enable intel AGP support (Intel 440LX/BX/GX, I8xx and E7x05 ...)
- or -
make sure you have only agpgart.ko module in /lib/modules/`uname -r`/kernel/drivers/char/agp:

THANKS! I now have a working suspend-to-disk on my Toshiba 2100 Pro (using Nvidia's 7676 driver). Suspend-to-ram still doesn't work but I don't think it's nvidia-related, cause it seems that the laptop doesn't wake up at all.